This invention relates to acoustic imaging catheters employing a rotating transducer.
It has long been recognized that acoustic imaging by use of internal probes has potential use in visualizing conditions of a body.
For example, Brown et al., U.S. Pat. No. 2,949,910, describes a catheter within a heart which detects heart size by a fixed transducer which emits sound waves and detects the echo return; Bom, U.S. Pat. No. 3,938,502, describes an ultrasonic device to be placed within a heart, comprising a catheter of 3 mm outer diameter having a plurality of fixed transducers. Peronneau, U.S. Pat. No. 3,542,014, describes a catheter having a piezoelectric transducer for measuring the size of a blood vessel; Frazer, U.S. Pat. No. 4,176,662, describes an endoscope employing a transmitter of ultrasonic energy waves so that its position within a body can be determined; Green et al., U.S. Pat. No. 4,327,738, describe an endoscope, having a transducer which is inserted into a body cavity such the stomach; Trimmer et al., U.S. Pat. No. 4,431,006, and Leeny et al., UKA 2,175,828, describe solid needles, for detecting sound waves, which may be inserted within a body; Silverstein et al., U.S. Pat. No. 4,462,408, describe an endoscope having an array of ultrasonic transducers which can be inserted into a body cavity such, as the stomach; and Pourcelot et al., U.S. Pat. No. 4,605,009, describe an endoscopic probe suitable for studying coronary arteries. Other internal probes have been proposed which cause movement of the ultrasonic beam to produce images of body features, of which the following are examples.
Eggleton et al., U.S. Pat. No. 3,779,234, describes an ultrasonic catheter for placement through an esophagus or chest wall. The catheter rotates at 360 rpm and has four transducers each having a diameter of 5 mm. The transducers are focused horizontally with an effective depth of penetration of about 15 cm. The housing of the catheter rotates and "may be a flexible stainless steel shaft constructed of right and left helices to maximize the torsional stiffness of the rotating assembly with the stationary housing. [such as produced by S. S. White and Company]".
Baba, U.S. Pat. No. 4,374,525, describes an ultrasonic device which may be placed within a body cavity and against a body wall. The transducers are rotated at between 500-900 rpm. The inserted section is generally rigid, but flexible enough to be placed against a body wall.
Suwaki et al., U.S. Pat. No. 4,375,818, describe an endoscope having an ultrasonic transducer suitable for positioning within a celiac cavity. The transducer can be rocked by a drive motor adjacent to it.
Ando et al., U.S. Pat. No. 4,391,282, describe an ultrasonic apparatus for celiac cavity insertion, for examination of the heart and pancreas. "[A] flexible power transmission member such as a coil wire or the like . . . " is provided.
Nakada et al., U.S. Pat. No. 4,558,706, describe an ultrasonic and optical device. The ultrasonic pulse is rotated by a mirror held on a "soft shaft formed of two inside and outside wound layer coils. These inside and outside coils are wound reversely to each other so that the outside diameter will not vary with the rotating direction and the rotation will be able to be effectively transmitted when curved." Gas bubbles generated within the catheter are removed through a conduit passing from the housing chamber to an outside chamber.
Kondo et al., U.S. Pat. No. 4,572,201, describe an intraluminal ultrasonic scanner which can be inserted into the stomach or pancreas The transducer is secured to a rotary shaft connected to a flexible shaft.
Andou et al., U.S. Pat. No. 4,674,515, describe an ultrasonic endoscope suitable for placement in a body cavity.
DE 3,619,195, appears to describe an ultrasonic catheter with a coil-spring driven magnet, which, by magnetic coupling, in turn causes rotation of a transducer.
Others previously have suggested employing miniature ultrasonic catheters to sense the wall thickness of blood vessels from within the vessel. Such suggestions have included rotatable catheters and sensing the rotation to provide so-called B-mode images of wall thickness.
Wider effective use of acoustic imaging would occur, especially in the vascular system, if such a system could be considerably smaller, have good image fidelity, and be simple, inexpensive and dependable.